The display is a major power consumer on mobile platforms. Content adaptive backlight power saving technology saves display backlight power by dynamically dimming display backlighting and enhancing pixel brightness at the same time to achieve the same perceived brightness and image fidelity. The backlight dimming level depends on a pixel brightness analysis, which can be done through various methods, such as histogram analysis based on the V value in HSV color space. Image brightness changes cause backlight and pixel adjustment.
If the transition of backlight and pixel brightness is not properly implemented, then temporal artifacts such as flicker or rolling artifact will be observed. For example, if backlight and pixel brightness changes are not synchronized, then flicker will be observed.
However, even if the backlight and pixel change are well synchronized, if the change is applied instantly, then flicker will be observed in the unchanged area during partial screen update. An example of such a case is playing video in a big window (but not full screen) and the unchanged area is bright. If the backlight and pixel change are applied instantly, there will be flicker in the unchanged area.
Applying a small relative percentage change every frame for both backlight and pixel change can help mitigate the flicker issue. That is why gradual or progressive change over time, called phase-in, has been implemented in the display power saving technology.